Preventing the spread of sexually transmitted diseases hinges on a full understanding of the array of factors that link the causal chain of acquisition and transmission of infection. The primary objective of the proposed research is to test a social-behavioral model of STD acquisition among adult men in the U.S. Within this broad objective, the specific aims of the proposed study are to: (1) identify the social, demographic, and contextual risk markers of STDs in the study population; (2) identify the behavioral risk factors of STDs in the study population; (3) examine the relationships between the risk markers and the risk factors; and, (4) estimate the effects of behavioral risk factors on the likelihood of STD acquisition. The conceptual model guiding the proposed research posits that the acquisition of an STD is a function of the probability of exposure to infection, the probability of infection if exposed, and the probability of disease if infected. Sexual and health care behaviors are risk factors that determine the outcome (STD acquisition) through these parameters. Social, demographic, and contextual risk markers influence both sexual behavior and health care behavior. Even though these risk markers operate primarily through the more proximate risk factors, they are important to consider because they constitute targets for behavioral intervention. Two corollary objectives of the proposed research are to examine the determinants of health care and sexual behavior following an STD infection, and to identify target populations for behavioral interventions aimed at reducing the acquisition and transmission of STDs. The objectives of the proposed research will be accomplished using data from a nationally representative survey of adult men in the U.S. The survey of 3,321 males aged 20-39 was conducted in 1991. The survey's breadth of coverage of sexual and health care behaviors, and STD histories, provide a unique opportunity to apply a social-behavioral model to an epidemiological mechanism of disease acquisition.